Coil coating is a continuous, automated process for coating metal with a primer, a bottom coat of paint, or a top coat of paint before fabrication into end products. The metal substrate, typically steel or aluminum, is delivered in coil form from a rolling mill. The metal coil is positioned at the beginning of a coating line, and in one continuous process, the coil is unwound, pre-cleaned, pre-treated, pre-primed, and pre-painted, typically using roller coating, before being recoiled at the end of the coating line and packaged for shipment. This process can be performed at up to about 213 meters (700 feet) per second.
Conventional coil coating paints (referred to herein as “coating compositions”) suffer from several drawbacks. For example, corrosion of the metal after coating is an on-going problem. ASTM D3794-13 describes a collection of methods used within the coil coatings industry to test for corrosion resistance. One such method is salt-spray testing, where the coated coil is sprayed with a salt solution for a period of time. Prior art coatings may only resist corrosion in such salt spray for a time period of less than 24 hours, which is undesirably short. Moreover, another such method is methyl-ethyl-ketone (MEK) “rubbing”, where the coated coil is rubbed with MEK solvent. Prior art coatings may only resist corrosion against such rubbing for less than ten rubs, which is undesirably few.
Accordingly, it is desirable to provide a coil coating composition with a relatively high solids content that exhibits improved corrosion resistance after the coil coating process (for example, greater than 1000 hours salt spray resistance, and greater than 200 MEK rubs resistance). In addition, it is desirable to provide a method for manufacturing such a coating composition. It also is desirable to provide a coil coating process using such a coating composition. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.